The Ecstasy is plenty capable of modern metal tones on the red channel. There's this idea floating around on the internet that the Ecstasy is somehow not suitable for modern metal; that's silly. There's more than enough gain on tap. Hell, I've gotten great metal tones out of the Shiva, which has less gain and a more "vintage" voicing than the Ecstasy.
The voicing isn't for everyone, I'll say that. It's fairly dark, with very thick mids. It's not Engl Powerball or VHT UL tight, either... but neither is an un-boosted Recto or a stock JCM 800. Unless you're Fear Factory or Meshuggah and need the absolute driest, tightest tone on the planet, it'll be fine. It's thick, warm, saturated gain. Some find the Ecstasy too smooth, but that's nothing treble/presence/EQ/boosting can't take care of.
The cleans are good, better than most. The mid-gain tones, if you need 'em, are phenominal. If you like dark, thick gain, the Ecstasy will get you there.
I love 'em, every time I've played one. Megadeth7684, if he still posts here, had an Ecstasy Classic for a while. If I recall correctly, he said it's the best amp he'd ever played, and that it would do Arch Enemy, etc. with ease.
As far as the difference between the models, the 101A is 6L6 and fairly rare. The 101B is the most common model; it's EL34. The Ecstasy Classic has a brighter, more open voicing compared to the darker, more compressed tones from the 101B. I've only played 101Bs, so take that for what it's worth. I've seen 101Bs go for as little as $1800 USD used; usually they're more in the $2-2.5k range. They're expensive bastards.